Process of treating metal surfaces with acid solutions



Z02. UUMIUSI l IUNS,

Patented Feb. 2, 1932 UNITED STATES r m ml I n12 PATENT OFFICE JAMES C. 'VIGNOS, F NITRO, WEST VIRGINIA, ASSIGNOB TO THE RUBBER SERVICE LABORATORIES GOMPANY, OF AKRON, OHIO, A CORPORATION OF OHIO PROCESS OF TREATING METAL SUB-FACES WITH ACID SOLUTIONS No Drawing.

This invention relates to the process of pickling metals, particularly iron and steel, in a pickle bath and comprises the provision of a regulator for causing the acid of the pickle bath selectively to attack the unclean portions of the metallic surface while substantially preventing the clean portions of the metal surface from deterioration by further action of the acid solution thereon. The invention, however, is useful in many other ways, such as for preventing substantial loss of metal processes for cleaning or freeing metals such as iron or steel in any form from rust or oxides or for removing scale, such as boiler scale and the like from sheets or tubes.

In the pickling process, iron and steel wire, sheets and other products which have become coated with a scale of iron oxide during the process of manufacture are submitted to treatment with dilute acid in order to remove the scale therefrom. The complete removal of the scale is necessary before any finishing process can be applied to the metal. The action of the acid in the pickling bath is to dissolve the scale, but unless means are present or troublesome manipulative precautions are taken to prevent further solvent action of the acid on the metal, this secondary action causes a pit-ting or roughening of the surface of the metal.

Among the S!,l,bstances heretofore proposed for use as inhibitors in the pickle process are the aldehydes and particularly the aliphatic aldehyde's'f The best known of such com- 35 pounds, however, are so readily vaporized at the temperature at which the pickling process is carried out, that a portion of the volatile inhibitor is constantly removed from the pickle liquor. Not only is the presence of 40 such pungent vapors obnoxious to workmen in the room, but the wastefulness accompanying the use of these materials has practically precluded the commercial application of this class of compounds in the pickling operation.

It has now been found that the many disadvantages attendant upon the use of aldehydes may be overcome and greatly improved results obtained if derivatives of aldehydes possessing relativelyhi'gh"boiling points be Application filed January 14, 1928. Serial No. 246,916.

employed in place of the more volatile aldehydes as inhibitors in the process set forth. Such high boiling derivatives preferably are sulphurized aldehyde compounds, such as the tri-thio-aldehydes, the oxidation products of thio-aldehydes, that is the sulphones, and other products such as the thialdines and the like. Moreover,-the sulphurized derivatives of the aldehydes have been found to be much more active as inhibitors than are the aldehydes themselves. Thus, for example, when tri-thio-furfuraldehyde was employed as an inhibitor in the pickling process, it was found that the loss of iron due to the action of acid on the iron sheets was only approximately one-seventh as great as that resulting when five times as much furfuraldehyde was employed under similar conditions as an inhibitor. Similar savings in iron loss were also realized by the use of tri-thio-crotonaldehyde and tri-thio-benzaldehyde.

The use of the preferred type of inhibitors will be understood from the following examples of the process. In the example, conditions were employed which duplicated, so far as possible, those commonly followed in commercial practice, so far as concerned acid concentrations and temperatures employed. The period of heating the metallic test strips in the pickling liquor was, however, from three 30 to four times that ordinarily followed in usual practice for the acid concentrations employed. This variation in practice was made in order to increase the severity of the test to which the materials were sub]ected. The following 5 is one preferred means of carrying out the tests hereinbefore referred to.

Test pieces of steel approximately three inches square were cut from a sheet after the annealing process had been carried out. The steel employed had a carbon content of approximately 0.04%. These pieces were then immersed in approximately 50 sulphilrinaciisg lltion containing approximately 8% by weight of 66 Baum acid together with approximately 0.05 grams of trithio-formaldehyde as an inhibitor. The test pieces were then subjected to the action of the pickle liquor for an hour while maintaining a temperature of from 176 to 185 F.

(80 to 85 C.) in the bath. For this acid concentration, commercial practice is to pickle at approximately 165 F. (736 C.) for from 15 to 20 minutes. Blank tests were also carried out simultaneously with and similar in every respect to those described except that no inhibitor was added to the pickle liquor. After the pickling test had been completed the test pieces were weighed and the loss in weight ascertained. It was found that the loss in weight suffered by the iron pieces in tests where the inhibitor was employed was approximately only 6% of the loss taking place when no inhibitor was employed. Increasing the quantity of tri-thio-formaldehyde from .05 grams as in the test described to 0.10 grams did not appear to afl'ect or improve the inhibiting efl'ects in any material manner.

By carrying out similar tests wherein 0.05 grams of tri-thio-acetaldehyde was employed as an inhibitor in approximately 500 cc. of 8% sulphuric acid solution, it was found that the loss in weight suffered by the steel test pieces was only about 7.8% as great as the loss taking place when no inhibitor was added to the acid solution. Expressed in other terms, this result shows that the solvent action of the pickle liquor upon iron by the addition to the pickle liquor of about 0.01% its weight of a tri-thio-aldehyde is reduced to approximately 1/14 that to be expected.

Derivatives of tri-thio-aldehydes have also been found to exert an equally favorable action in the metal pickling process. Thus, sulphones and the ammonia derivatives of trithio-aldehydes are effective inhibitors of the solvent action of acids upon metals. Thialdine, that is the hydrogen sulfid derivative of aldehyde ammonia, when employed in sulphuric acid solution in the proportion of less than 0.1% of the weight of the acid solution taken was found to effect a saving of about 13/14 of the loss caused by employing in a pickling process an acid of the same concentration but containing no inhibitor. In other words, the loss in the pickling step due to the solvent action of the acid upon the metal, because of the presence of less than 0.1% by weight of the inhibitor in the acid solution employed, is but approximately 8% of the loss produced by a solution of the same acid concentration but containing no inhibitor.

From the results hereinbefore set forth, it is evident that tri-thio-aldehydes and derlvatives thereof comprise a class of effective inhibitors in processes wherein metals are subjected to the action of an acid. Greater inhibiting action has been found in general to be produced by the use of a larger quantity of the various compounds than those particularly set forth in the example. Although such compounds may be employed in any proportion desired up to the limit of their solubilities in the acid solution. it. is nmmllv nrn-F- erable when operating on a commercial scale to employ an acid solution containing less than 1% of inhibitor.

Equally characteristic results are shown by the use of other acids, such as hydrochloric and nitric acids in the pickle liquor and also in the treatment of other metals. Thus copper, bronzes and alloys of other metals will likewise be protected against undue acid solvent action by carrying out the pickling operation in the presence of one of the preferred type of inhibitors set forth.

The examples hereinbefore set forth are to be understood as illustrative only and notat all limitative of the scope of the invention. Other examples of the use of the process are apparent to those skilled in the art to which the invention pertains wherein different acid concentrations, times of treatment and temperatures may be employed. The invention is to be considered as limited solely by the following claims wherein the invention is claimed as broadly as is possible in view of the prior art.

\Vhat is claimed is:

1. A metal treating compound comprising a non-oxidizing acid solution containing from 0.05 to 1% of thialdine.

2. A metal treating compound comprising a sulphuric acid solution containing from 0.05 to 0.1% of thialdine.

3. The process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of sulphuric acid containing dissolved thialdine.

4. A metal treating compound comprising a non-oxidizing acid solution containing from 0.05 to 1.0% of an ammonia derivative of a thio aldehyde.

5. A metal treating compound comprising a non-oxidizing acid solution containing from 0.05 to 0.1% 01 an ammonia derivative of a tri-thio aliphatic aldehyde.

6. The process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a solution containing an ammonia derivative of a thio aldehyde dissolved in a non-oxidizing acid.

7. The process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a solution containing an ammonia derivative of a trithio aliphatic aldehyde dissolved in a nonoxidizing acid.

In testimony whereof I hereunto affix my signature.

JAMES C. VIGNOS. 

